King Louis XIV issued in 1661 a decree determining merchant ships should fly a blue ensign with a white cross, charged with the royal arms. A white cross on blue field had been common from long ago, but by the end of 17th century started declining into disuse, because merchant ships favoured white flags like those of Royal Navy. Despite all prohibitions, this usurpation had become generalized around 1760 and officialized by the Order of 25 March 1765.

In the case of Laurent de Graff, however, it's quite likely he constrained himself to fly a regulation merchant ensign, so as to masquerade as an innocent trader. What is attested indeed is his use of yellow-red striped, and white fleurdelisée flags (these latter, with either one or three fleurs-de-lis), at least in his 1683 attack on Veracruz (Mexico). These were apparently used on land but I've also guessed their hypothetical use at sea as jacks or mast flags.